Quantitating Diffusion Enhancement in Pore Hierarchies.

A microporous continuum traversed by a set of mutually perpendicular channels is considered to be a model for a hierarchically porous system of the mesoporous zeolite type. Transient profiles of molecular uptake as determined by kinetic Monte Carlo (kMC) simulation are found to be in excellent agreement with the result attained by the application of the two-region model (the Kärger model) of molecular diffusion. In particular, it is found that, in the two limiting cases referred to as fast exchange and slow exchange, there exist two simple analytical expressions for the rate of molecular uptake and hence for the quantification of transport enhancement in comparison with the purely microporous adsorbent. In the general case, transport enhancement is simply recognized by the reciprocal addition of the expressions in the two limiting cases.

Liquid-liquid transition in supercooled gallium alloys under nanoconfinement.

NMR studies of the thermal evolution of the Ga-In-Sn and Ga-In liquid alloys embedded into opal matrices were carried out. Temperature dependences of the gallium lineshape, shift of the resonance frequency (Knight shift), and intensity were obtained upon cooling down to the alloy freezing and subsequent warming. A second high-frequency 71Ga NMR signal emerged for both alloys upon cooling, the NMR line intensity transferring gradually into this additional signal. The Knight shifts of the signals differed noticeably. The transformations of the gallium line upon warming were continuous and not affected by changes in the alloy compositions induced by melting. 115In NMR measurements were conducted to monitor the alloy compositions at freezing and melting. The findings suggest the occurrence of the liquid-liquid phase transition in the strongly supercooled alloys under nanoconfinement.

Soft Quantum Control for Highly Selective Interactions among Joint Quantum Systems.

We propose a quantum control scheme aimed at interacting systems that gives rise to highly selective coupling among their near-to-resonance constituents. Our protocol implements temporal control of the interaction strength, switching it on and off again adiabatically. This soft temporal modulation significantly suppresses off-resonant contributions in the interactions. Among the applications of our method we show that it allows us to perform an efficient rotating-wave approximation in a wide parameter regime, the elimination of side peaks in quantum sensing experiments, and selective high-fidelity entanglement gates on nuclear spins with close frequencies. We apply our theory to nitrogen-vacancy centers in diamond and demonstrate the possibility for the detection of weak electron-nuclear coupling under the presence of strong perturbations.

Controllable Non-Markovianity for a Spin Qubit in Diamond.

We present a flexible scheme to realize non-Markovian dynamics of an electronic spin qubit, using a nitrogen-vacancy center in diamond where the inherent nitrogen spin serves as a regulator of the dynamics. By changing the population of the nitrogen spin, we show that we can smoothly tune the non-Markovianity of the electron spin's dynamics. Furthermore, we examine the decoherence dynamics induced by the spin bath to exclude other sources of non-Markovianity. The amount of collected measurement data is kept at a minimum by employing Bayesian data analysis. This allows for a precise quantification of the parameters involved in the description of the dynamics and a prediction of so far unobserved data points.

Surface enhanced infrared absorption of chemisorbed carbon monoxide using plasmonic nanoantennas.

We report the enhancement of infrared absorption of chemisorbed carbon monoxide on platinum in the gap of plasmonic nanoantennas. Our method is based on the self-assembled formation of platinum nanoislands on nanoscopic dipole antenna arrays manufactured via electron beam lithography. We employ systematic variations of the plasmonic antenna resonance to precisely couple to the molecular stretch vibration of carbon monoxide adsorbed on the platinum nanoislands. Ultimately, we reach more than 1500-fold infrared absorption enhancements, allowing for an ultrasensitive detection of a monolayer of chemisorbed carbon monoxide. The developed procedure can be adapted to other metal adsorbents and molecular species and could be utilized for coverage sensing in surface catalytic reactions.

Field-stepped broadband NMR in pulsed magnets and application to SrCu2(BO3)2 at 54T.

Pulsed magnets generate the highest magnetic fields as brief transients during which the observation of NMR is difficult, however, this is the only route to unique insight into material properties up to the regime of 100T. Here, it is shown how rather broad NMR spectra can be assembled in a pulsed magnet during a single field pulse by using the inherent time dependence of the field for the recording of field-stepped free induction decays that cover a broad frequency range. The technique is then applied to (11)B NMR of the spin-dimer system SrCu2(BO3)2, a magnetic insulator known to undergo a series of field-driven changes of the magnetic ground state. At peak fields of about 54T at the Dresden High Magnetic Field Laboratory, (11)B NMR spectra spanning a total of about 9MHz width are reconstructed. The results are in good accordance with a change from a high-temperature paramagnetic state to a low-temperature commensurate superstructure of field-induced spin-dimer triplets.

NMR shift and relaxation measurements in pulsed high-field magnets up to 58T.

Nuclear magnetic resonance (NMR) experiments at fields up to 58T in pulsed magnets at the Dresden High Magnetic Field Laboratory are reported. The challenge to resolve NMR shifts in these time-dependent fields is addressed for the first time, and it is shown that this can indeed be accomplished with high precision with an internal reference. As a result, signal averaging is possible during a single magnetic field pulse, but also for multiple pulses. Thus, even very weak signals can in principle be recorded and their shifts can be determined. In a second set of experiments, the measurement of nuclear relaxation is investigated. Using adiabatic inversion with the inherent time dependence of the magnetic field and small-angle inspection, it is shown that relaxation measurements are possible, as well. The shift experiments were performed with (27)Al NMR on a mixture of aluminum metal and a Linde type A zeolite. For the relaxation studies, (27)Al NMR and (69)Ga NMR on the metals aluminum and gallium were preformed, respectively.

Polymorphism of Metallic Sodium under Nanoconfinement.

(23)Na NMR studies of sodium nanoparticles confined to porous glass with the 3.5 nm mean pore size were carried out. The emergence of the second component of the NMR line was observed below 240 K that evidences the occurrence of another modification of metallic sodium. The phase transition temperature is much higher than the martensite transformation temperature in bulk sodium.

Diffusion and Molecular Exchange in Hollow Core-Shell Silica Nanoparticles.

The diffusion behavior of small molecules in hollow core-shell nanocapsules was studied using pulsed field gradient NMR. By purposefully selecting the liquid saturating the hollow core and the porous shell and the solvent between the nanocapsules, two different situations corresponding to the excluded and admitted molecular exchange between the intra- and intercapsule liquids at the external boundary of the nanoparticles were covered. In the former case, corresponding to the reflective boundary condition for the molecules approaching the nanocapsule boundary, restricted diffusion in the complex pore space formed by the hollow core and the mesoporous shell was observed. The time-dependent diffusivities measured in the experiment were inter-related with the geometry of the intraparticle pore space. The thus assessed structural information was found to be in a good agreement with that provided by electron microscopy. In the case of the molecular exchange occurring between the two pools of molecules in the nanocapsules and between them, the diffusive dynamics of only the molecules remaining in the nanocapsules during the entire observation times was studied.

High-sensitivity NMR beyond 200,000 atmospheres of pressure.

Pressure-induced changes in the chemical or electronic structure of solids require pressures well into the Giga-Pascal (GPa) range due to the strong bonding. Anvil cell designs can reach such pressures, but their small and mostly inaccessible sample chamber has severely hampered NMR experiments in the past. With a new cell design that has a radio frequency (RF) micro-coil in the high pressure chamber, NMR experiments beyond 20 Giga-Pascal are reported for the first time. (1)H NMR of water shows sensitivity and resolution obtained with the cells, and (63)Cu NMR on a cuprate superconductor (YBa2Cu3O7-δ) demonstrates that single-crystals can be investigated, as well. (115)In NMR of the ternary chalcogenide AgInTe2 discovers an insulator-metal transition with shift and relaxation measurements. The pressure cells can be mounted easily on standard NMR probes that fit commercial wide-bore magnets with regular cryostats for field- and temperature-dependent measurements ready for many applications in physics and chemistry.

63Cu nuclear magnetic resonance study of Pr(1.85)Ce(0.15)Cu(1-x)Ni(x)O(4): Ni-induced spin density oscillation and modification of the low energy spin fluctuations.

We report the results from a (63)Cu nuclear magnetic resonance (NMR) study of the electron-doped high temperature superconducting cuprate (HTSC) Pr(1.85)Ce(0.15)Cu(1-x)Ni(x)O(4). We find that Ni induces a magnetic broadening of the (63)Cu NMR spectra that can be interpreted in terms of an induced spin density oscillation about the Ni site, similar to that reported from (63)Cu NMR measurements on the hole-doped HTSCs when Zn is partially substituted for Cu. There is also an additional temperature-dependent contribution to the (63)Cu spin-lattice relaxation rate that can be interpreted in terms of an Ni-induced modification of the low energy spin fluctuations. Furthermore, the spin fluctuations are intrinsically spatially inhomogeneous and additional inhomogeneities are induced by Ni.

DNA relaxation dynamics as a probe for the intracellular environment.

Investigations into the biophysical properties of single molecules traditionally involve well defined in vitro systems where parameters such as solvent viscosity and applied forces are known a priori. These systems provide means to develop models describing the polymers response to a variety of conditions, including the entropically driven relaxation of a stretched biopolymer upon release of the tension inducing force. While these techniques have proven instrumental for recent advancements in the fields of polymer physics and biophysics, how applicable they are to life inside the cell remains poorly understood. Here we report an investigation of in vivo stretched polymer relaxation dynamics using chromatin relaxation following the breakage of a dicentric chromosome subjected to microtubule-based spindle forces. Additionally, we have developed an in vitro system used to verify the conformations observed during the in vivo relaxation, including the predicted but previously unidentified taut conformation. These observations motivate our use of existing polymer models to determine both the in vivo viscosity as seen by the relaxing chromatin and the tension force applied by the microtubule-based spindle in vivo. As a result, the technique described herein may be used as a biophysical strategy to probe the intranuclear environment.

Evidence for two electronic components in high-temperature superconductivity from NMR.

A new analysis of (63)Cu and (17)O NMR shift data on La(1.85)Sr(0.15)CuO(4) is reported that supports earlier work arguing for a two-component description of La(1.85)Sr(0.15)CuO(4), but conflicts with the widely held view that the cuprates are a one-component system. The data are analyzed in terms of two components A and B with susceptibilities χ(AA), χ(AB)(= χ(BA)) and χ(BB). We find that above T(c), χ(AB) and χ(BB) are independent of temperature and obtain for the first time the temperature dependence of all three susceptibilities above T(c) as well as the complete temperature dependence of χ(AA)+χ(AB) and χ(AB)+χ(BB) below T(c). The form of the results agrees with that recently proposed by Barzykin and Pines.

Increased basal-ganglia activation performing a non-dystonia-related task in focal dystonia.

BACKGROUND AND PURPOSE: We tried to determine whether altered sensorimotor cortex and basal-ganglia activation in blepharospasm (BSP) and cervical dystonia (CD) are restricted to areas directly responsible for the innervation of dystonic muscles, or whether impairment in focal dystonia reaches beyond these direct associations supporting a more global disturbance of sensory and motor control in focal dystonia. METHODS: Twenty patients with focal dystonia (11 BSP, 9 CD) and 14 healthy controls were investigated with functional magnetic resonance imaging (fMRI) performing a simple grip force forearm contraction task. RESULTS: BSP and CD patients and healthy controls showed similar activation in the pre-motor, primary motor and primary sensory cortex, whilst basal-ganglia activation was increased in BSP and CD with related activation patterns compared with controls. BSP patients had increased activation in the thalamus, caudate nucleus, putamen and lateral globus pallidus, whilst CD patients showed increased activation in the caudate nucleus, putamen and thalamus. No differences in applied grip force were detected between groups. CONCLUSIONS: In both, BSP and CD, increased basal-ganglia activation could be demonstrated in a task not primarily involving the dystonic musculature affected by these disorders. Comparable activation changes may also indicate a common pathway in the pathophysiology in BSP and CD.

Carpal tunnel syndrome--a comprehensive review.

PURPOSE: To provide a comprehensive review of the management of carpal tunnel syndrome. METHODS AND RESULTS: A systematic literature review is provided of the history, anatomy, pathophysiology, epidemiology, diagnostic criteria, investigative surgical techniques, results and complications for carpal tunnel syndrome. CONCLUSION: Surgery for carpal tunnel syndrome requires meticulous attention to history-taking, investigation, counseling, training and surgical technique if unsatisfactory results and complications are to be avoided.

Albuminuria, intermittent hyperfiltration and salt wasting in patients with stroke: a pilot study.

OBJECTIVE: To investigate whether different types of stroke influence renal excretion of albumin, major electrolytes and water. MATERIAL AND METHODS: Timed urine collections were started shortly after admission in 5 patients with haemorrhagic stroke (group A), 5 with ischaemic stroke (group Bx), 6 with presumed ischaemic stroke (groups By/z) and 6 with subarachnoid haemorrhage (group C). Albuminuria was also investigated in four patients undergoing elective abdominal surgery. RESULTS: Increased levels of albuminuria were observed in all patients in groups A and B, but were found to decline with observation time and appeared to be related to outcome in group B. In group C, albuminuria was detected in 4 out of 6 patients. Elective surgery did not affect albumin excretion. In a setting with high urinary osmolality, high excretion rates for creatinine, urea, sodium, potassium and large diuresis were intermittently observed in groups A, B and C. None of these patients was in steady-state condition. CONCLUSIONS: Different types of stroke elicit a complex change in renal function which resembles the response to a hypervolaemic and hyperosmolar signal, possibly mediated by a breakdown of renal autoregulation of blood flow in the presence of high vasopressin activity. Acute changes in excretion of albumin might be an indicator of prognosis in stroke. The findings point to the existence of unrecognized pathways between the central nervous system and the kidneys. Further studies on the mechanisms underlying alterations in renal function in stroke and their implication for treatment and outcome are indicated.

Sperm donation: implications of Canada's Assisted Human Reproduction Act 2004 for recipients, donors, health professionals, and institutions.

BACKGROUND: On April 22, 2004, the Assisted Human Reproduction Act came into force, prohibiting the purchase of sperm or eggs from donors in Canada. In response to the concerns of medical professionals and some consumers that prohibiting payment would lead to a decline in the number of gamete donors, Health Canada commissioned research on altruistic donor recruitment and recruitment strategies. METHODS: Twenty-two studies of sperm donors were located and their findings reviewed. The studies spanned 23 years (1980-2003), were undertaken in a range of countries, and were chosen on the merit of their relevance to the development of recruitment strategies within a policy of altruistic sperm donation. Observations were derived from assessing and comparing the purposes, findings, and implications of the 22 studies. RESULTS: Payment for providing sperm was made in all but three studies, although participants in 15 studies indicated clearly that their motivations were primarily altruistic. Observations indicate that men who are more willing to be identified to offspring in the future share demographic characteristics, such as age and parental status, with those who are prepared to donate altruistically. These characteristics appear to be a factor in motivation to donate altruistically. CONCLUSION: The studies show that there are men who are prepared to donate sperm without financial payment. The findings suggest that a change is required in the culture of sperm donation, specifically the adoption of a new approach to donor recruitment.

Thin-foil magnetic force system for high-numerical-aperture microscopy.

Forces play a key role in a wide range of biological phenomena from single-protein conformational dynamics to transcription and cell division, to name a few. The majority of existing microbiological force application methods can be divided into two categories: those that can apply relatively high forces through the use of a physical connection to a probe and those that apply smaller forces with a detached probe. Existing magnetic manipulators utilizing high fields and high field gradients have been able to reduce this gap in maximum applicable force, but the size of such devices has limited their use in applications where high force and high-numerical-aperture (NA) microscopy must be combined. We have developed a magnetic manipulation system that is capable of applying forces in excess of 700 pN on a 1 mum paramagnetic particle and 13 nN on a 4.5 mum paramagnetic particle, forces over the full 4pi sr, and a bandwidth in excess of 3 kHz while remaining compatible with a commercially available high-NA microscope objective. Our system design separates the pole tips from the flux coils so that the magnetic-field geometry at the sample is determined by removable thin-foil pole plates, allowing easy change from experiment to experiment. In addition, we have combined the magnetic manipulator with a feedback-enhanced, high-resolution (2.4 nm), high-bandwidth (10 kHz), long-range (100 mum xyz range) laser tracking system. We demonstrate the usefulness of this system in a study of the role of forces in higher-order chromosome structure and function.

[Long-term fate of left atrial thrombi and incidence of cerebral embolism under continuous anticoagulation therapy]. / MR-tomographische Evaluation der Inzidenz zerebraler Embolien bei Patienten mit Vorhofflimmern und linksatrialen Thromben.

PURPOSE: Patients (pts.) with atrial fibrillation (AF) and atrial thrombi are known to have an increased risk for cerebral embolism. However, little is known about the clinical course of atrial thrombi and the incidence of cerebral embolism in those patients during anticoagulation therapy. The high sensitivity of MR imaging (MRI) including diffusion-weighted imaging (DWI) suggests that this technique could provide an improved estimate of cerebral embolism associated with the presence of left atrial thrombi. The aims of this prospective study were to evaluate 1) the prevalence of clinically silent and apparent cerebral embolism in pts. with newly diagnosed AF and atrial thrombi using MRI/DWI, 2) the long-term fate of atrial thrombi under continues anticoagulation therapy and 3) the incidence of cerebral embolism during a follow-up period of 12 months with continuous anticoagulation therapy. MATERIALS AND METHODS: The study group consisted of 32 pts. with 1) newly diagnosed AF and evidence of left atrial (LA) thrombi detected by TEE and 2) a new start of anticoagulation therapy [International Normalized Ratio (INR) 2.0 - 3.0]. 19 pts. with 1) newly diagnosed AF and no evidence of atrial thrombi and 2) an equivalent anticoagulation regimen served as the control group. In both groups a) MRI/DWI studies of the brain (weeks 0, 4, 8, 12, 20, 28, 36, 44, and 52), b) transesophageal echocardiographic studies (TEE) for assessment of LA-Thrombi (weeks 0 and 52) and c) clinical neurological assessments (weeks 0, 20 and 52) were performed. RESULTS: In the study group (AF and LA-Thrombi) 11 out of 32 pts. (34 %) displayed signs of acute (n = 8) or chronic (n = 3) cerebral embolism in the initial MRI studies. In 4 out of 32 pts. (13 %), MRI/DWI depicted new or additional cerebral emboli (n = 12) during the follow-up period despite continuous anticoagulation therapy. 2 (n = 2/4; 50 %) of these patients had clinically apparent neurological deficits. In the control group 1 out of 19 pts. (5 %) showed evidence of chronic cerebral embolism as assessed by MRI/DWI at the beginning of the study (week 0). No embolic cerebral lesions were detected during the 12-month follow-up. Within 12 months only 63 % (n = 20/32) of LA thrombi in the study group resolved completely under anticoagulation. CONCLUSION: 1. The incidence of clinically inapparent cerebral emboli in pts. with newly diagnosed AF and atrial thrombi is much higher than the incidence of clinically apparent emboli and has been underestimated in the past. 2. New cerebral embolism may occur even with continued effective anticoagulation therapy in 13 % of pts. 3. Only 63 % of atrial thrombi resolve completely within 12 months under anticoagulation therapy.